cmake: Fix riscv-gnu toolchain file. #24305
cmake(3.22.1) failed without the keyword `PATHS` on my device when I manually set `TOOLCHAIN_COMPILER_LOCATION_HINT` in command. And this patch is going to fix this issue.
[CMake Doc](https://cmake.org/cmake/help/latest/command/find_program.html):
> find_program (
> <VAR>
> name | NAMES name1 [name2 ...] [NAMES_PER_DIR]
> [HINTS [path | ENV var]... ]
> [PATHS [path | ENV var]... ]
### Pull Request Readiness Checklist
See details at https://github.com/opencv/opencv/wiki/How_to_contribute#making-a-good-pull-request
- [ ] I agree to contribute to the project under Apache 2 License.
- [ ] To the best of my knowledge, the proposed patch is not based on a code under GPL or another license that is incompatible with OpenCV
- [ ] The PR is proposed to the proper branch
- [ ] There is a reference to the original bug report and related work
- [ ] There is accuracy test, performance test and test data in opencv_extra repository, if applicable
Patch to opencv_extra has the same branch name.
- [ ] The feature is well documented and sample code can be built with the project CMake
